WASHINGTON - The largest union representing federal workers on Thursday took the Trump administration to court to block a new executive order that severely restricts the time employees may spend on union activity, claiming the president's action violates the First Amendment and oversteps the president's constitutional authority.

"This president seems to think he is above the law, and we are not going to stand by while he tries to shred workers' rights," said the American Federation of Government Employees national president J. David Cox Sr., in a statement that announced the lawsuit, filed in U.S. District Court for the District.

"This is a democracy, not a dictatorship," Cox said. "No president should be able to undo a law he doesn't like through administrative fiat."

The White House did not immediately comment on the lawsuit.

The restriction on what is known as "official time" - which will ultimately have to be bargained through collective bargaining contracts at federal agencies - was one of three orders the president signed late Friday before the Memorial Day weekend to roll back long-held civil service protections for federal employees.

The others instruct agencies to crack down on unions in contract negotiations and move more aggressively to fire employees with records of misconduct or poor performance.

The lawsuit challenges the official time guarantee that Congress gave federal employee unions four decades ago.

AFGE, which represents about 700,000 federal workers, argues that the executive order violates the union's right to freedom of association, guaranteed by the First Amendment. The lawsuit claims the Trump administration has singled out labor organizations for disparate treatment.

AFGE also says that mandating the number of hours agencies may authorize for employees' use of official time to 25 percent illegally changes a provision of the law Congress passed in 1978 - the Civil Service Reform Act - that governs collective bargaining and determines that official time is lawful.

"Congress passed these laws to guarantee workers a collective voice in resolving workplace issues and improving the services they deliver to the public every day - whether it's caring for veterans, ensuring our air and water are safe, preventing illegal weapons and drugs from crossing our borders, or helping communities recover from hurricanes and other disasters," Cox said.

"We will not stand by and let this administration willfully violate the Constitution to score political points."